Investigation of turbulent structures in a supersonic free shear layer.
Item
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Title
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Investigation of turbulent structures in a supersonic free shear layer.
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Identifier
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AAI9224869
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identifier
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9224869
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Creator
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Zhang, Jianjun.
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Contributor
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Adviser: Joseph A. Johnson, III
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Fluid and Plasma
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Abstract
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The compressible, supersonic free shear layer is investigated experimentally in a Ludwieg tube-wind-tunnel. A new measurement technique based on laser induced fluorescence (LIF) is developed, by which simultaneous, multi-point local density and density fluctuation can be obtained in the supersonic free shear layer. From the density measurements, the streamwise and transverse velocity components are calculated. Density, velocity and turbulent intensity profiles and their evolution along the streamwise direction are measured. Large scale structures at inner layer are observed by both shadowgraph photograph and multi-point density measurements. The mean structure spacing, the spatial rate of changing and mean persistent time of the structures are determined. The spreading of the turbulent region of the shear layer is measured by means of velocity profiles obtained along streamwise locations. An analytical investigation of the shocklet provides a generalizable physical model for shocklet processes, which agrees with our experimental results. It is concluded that eddy shocklet is a transient shock wave generated from the interaction between the convecting eddy and environmental field which reduces the scale of turbulent structure, especially the spreading rate of the shear layer, and generates a vortical field extending into the main flow from the outer region of the shear layer. A connection of eddy shocklets with the streaky structures ejected from the lower layer is suggested with the strong compression between the structures, with slow convecting velocity, and the supersonic flow field generating the pressure field which forms the transient shock wave. The dynamical process of shocklet formation and propagation are observed to be the apparent basic agent for turbulent energy transfer between the inner and outer regions of the layer and also the eddy motion and environmental flow field, hence they contribute significantly to the entire turbulent process in shear layer.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
